1. Field of the Invention
This invention relates to a method of controlling a recording laser beam for recording information onto an optical recording medium.
2. Description of the Prior Art
In recent years, disc-shaped recording media such as optical discs or photomagnetic discs, etc. utilizing the optical or magneto-optical signal recording/playback method are being developed and delivered to the market. For such disc-shaped recording media, there are known a recording medium of the read only memory (ROM) type such as so called a compact disc (CD), etc., a recording medium of so called a write once type onto which data can be once written on the user side, a recording medium which can rewrite (overwrite) data such as a photomagnetic disc, etc., and the like.
In the optical disc recording/playback apparatuses adapted to implement writing or reading of data on write once type or overwritable optical discs, the optical disc is rotated at a fixed angular velocity or a fixed linear velocity by the spindle servo and focus servo and/or tracking servo are applied to the optical head. The optical head includes a laser diode driven by the laser drive circuit to output a laser beam for recording/playback of information, a photodetector for detecting a reflected light of the laser beam irradiated onto the optical disc, and the like. On the basis of a detected output by the photodetector the optical head scans recording tracks of the optical disc and uses the laser beam to carry out recording/playback of information.
Further, in the optical disc recording/playback apparatuses adapted to scan recording tracks by using a laser beam to carry out recording/playback of information in a manner stated above, there is the possibility that if the beam power of a laser beam scanning the recording tracks is too small at the time of the recording mode, information may not be securely recorded, and if the beam power of a laser beam scanning recording tracks is too large at the time of playback mode, a serious effect or influence such as destruction is exerted on information recorded on the recording tracks. For this reason, as in the apparatus disclosed in, e.g., the Japanese Patent Laid Open No. 46633/78, a technique is employed to carry out switching of a so called APC servo loop in dependency upon various operational modes, which is adapted to detect the intensity of a laser beam for recording/playback of information, i.e., light quantity to carry out a feedback control of the drive circuit for the laser diode outputting a laser beam to keep constant the beam power of the laser beam, thus to suitably carry out switching of the beam power.
In the conventional laser beam power control as described above, since only a control of a fixed, predetermined laser output is provided, the following problems occur. Namely, an optimum laser output for permitting recording in a reasonable pit form varies (1) by unevenness of characteristics between media, (2) by the spatial positional (inclined angular) relationship with respect to the optical system by skew (inclination), etc. of the medium, and (3) by changes in the recording characteristic of the medium due to temperature changes. For this reason, even if an approach is only employed to keep the laser output constant, formation of pits of an optimum dimension is not necessarily carried out.